ABSTRACT Breast cancer (BC) continues to be a serious health problem in the United States. The oncogene HER2/neu and the folate receptor alpha (FRa) are overexpressed in BC and validated targets for cancer therapeutics. The humanized IgG1 monoclonal antibody (Ab) trastuzumab (Herceptin) has been approved by the FDA for the treatment of advanced BC and several humanized IgG Abs to FRa are in clinical trials. However, their efficacy is limited and additional strategies to target HER2/neu and FRa overexpressing tumors are still urgently needed. Interestingly, high densities of mast cells (MC) in BC tumors are associated with favorable prognoses. We discovered that human adipose cells can be differentiated into autologous, fully functional MC capable of releasing anti-tumor mediators TNF-a and GM-CSF upon FceRI stimulation and inducing BC cell death. In addition, we have shown for the first time that primary human MC and their stem cell precursors can be transduced with a lentiviral vector carrying green fluorescence (GFP) protein opening up the possibility they could be transduced with other tumor killing molecules (e.g. TRAIL, granzyme, etc.) to create new ways to treat BC by directing immune evading cells with anti-tumor agents to tumors. However, it is important to determine if the ADMC will target cancer cells in vivo, determine the initial pharmacokinetics of this interaction, and establish proof-of-principle in regards to efficacy. Our overall hypothesis is ADMC can be transduced with genetic imaging modules that will allow for the visualization and quantification of binding to luciferase transduced BC cells/tumors in vivo after i.v. injection. Herein, we will use a novel and safer lentivirus vector system to transduce ADMC with genetic modules that will allow for in vivo visualization without affecting BC cell killing capabilities by comparing their ability to induce BC cell death compared to non-transduced ADMC. Further, we will visualize and quantify ADMC binding to BC cells in vivo and assess overt signs of toxicology activity in xenograft tumor models.